Oligomerization process

ABSTRACT

A liquid phase process for oligomerization of C 4  and C 5  isoolefins or the etherification thereof with C 1  to C 6  alcohols wherein the reactants are contacted in a reactor with a fixed bed acid cation exchange resin catalyst at an LHSV of 5 to 20, pressure of 0 to 400 psig and temperature of 120 to 300° F. wherein the improvement is the operation of the reactor at a pressure to maintain the reaction mixture at its boiling point whereby at least a portion but less than all of the reaction mixture is vaporized. By operating at the boiling point and allowing a portion of the reaction mixture to vaporize, the exothermic heat of reaction is dissipated by the formation of more boil up and the temperature in the reactor is controlled.

The Government of the United States of America has certain rights inthis invention pursuant to Contract No. DOE-FC07-800CS40454, awarded bythe U.S. Department of Energy.

This application is a divisional of Ser. No. 058,698, filed 6-01-87which is a continuation of Ser. No. 442,359 filed 11-17-82, nowabandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an improved process for carrying outliquid phase oligomerizations and etherifications in a fixed catalystbed.

2. Related Art

Recently a new method of conducting certain catalytic reactions has beendevised. Two particular reactions for which this method has beenparticularly useful are oligomerization and etherification of C₄ and C₅isoolefins. The method involved is briefly described as one whereconcurrent reaction and distillation occur in a combinationreactor-distillation column with the distillation structure serving asthe catalyst. This process and catalytic distillation structures aredescribed in several U.S. Pat. Nos., namely U.S. Pat. Nos. 4,242,530;4,250,052; 4,232,177; 4,302,356; 4,307,254; and 4,336,407.

This new system has been commercially applied to the production ofmethyl tertiary butyl ether (MTBE) produced by the reaction of isobutenecontained in C₄ refinery streams and methanol.

It is well known that primary alcohols will react preferentially withthe tertiary alkenes in the presence of an acid catalyst, for example,as taught in U.S. Pat. Nos. 3,121,124; 3,629,478; 3,634,534; 3,825,603;3,846,088; 4,071,567; and 4,198,530.

The catalytic distillation process differs from these older processes inthat a catalyst system was disclosed (U.S. Pat. Nos. 4,215,011 and4,302,356) which provided for both reaction and distillationconcurrently in the same reactor, at least in part within the catalystsystem. For example, in this system and procedure, methanol and anisobutene containing C₄ stream are continuously fed to thereactor/distillation column where they are contacted in the catalyticdistillation structure. The methanol preferentially reacts withisobutene, forming MTBE, which is heavier than the C₄ components of thefeed and the methanol, hence it drops in the column to form the bottoms.Concurrently, the unreacted C₄ 's (e.g. n-butane, n-butenes) are lighterand form an overhead.

The reaction just described is reversible, which means that it isnormally equilibrium limited, however, by removing the ether (MTBE) fromcontact with the catalyst (as a bottoms), the reaction is forced tocompletion (Le Chatelier Principle). Hence it can be run to obtain avery high conversion of the isobutene present (95%+). As a result, agreat deal of control over the rate of reaction and distribution ofproducts can be achieved by regulating the system pressure. The boilingpoint in the reactor is determined by the boiling point of the lowestboiling material (which could be an azeotrope) therein at any givenpressure. Thus at a constant pressure a change in the temperature at apoint within the column indicates a change in the composition of thematerial at that point. Thus to change the temperature in the column thepressure is changed for any given composition.

Since oligomerization and etherification are exothermic there is excessheat in the reactor. In the liquid phase system, methods were devised toremove this heat, since in the case of resin type catalysts excessivetemperature (hot spots) can damage the catalyst. In the catalyticdistillation the excess heat merely causes more boil up in the column.

In an unrelated area the volatilization of a portion of the feed in acatalytic C₃ hydrogenation to provide a quasiisothermal reactor isdiscussed in Chemical Engineering Progress, Vol 70, No. 1, January,1974, pages 74-80.

In addition to the catalytic distillation system, there are severalother etherification systems in commercial use or available which areliquid phase systems That is, these systems are operated underconditions of pressure to maintain the contents of the reactor in liquidphase. One other principal problems encountered in these systems is theexothermic heat of reaction. Heat is sometimes removed by using heatexchangers in the reactor, such as tubular reactors having a heatexchange medium contacting the tubes, other systems employ feed diluentsto maintain a low concentration of reactive isobutene. In other words,the temperature in the catalyst bed has to be controlled by the removalof excess heat in some manner.

The present invention which relates to the liquid phase type of reactionalso provides a means for removing heat from the fixed continuouscatalyst bed. It is a further advantage that the present type of liquidphase reaction may be used in conjunction with a catalytic distillationcolumn reactor to obtain very high conversions of iso C₄ and C₅ alkenesin the feed stream.

These and other advantages will become apparent from the followingdescriptions.

SUMMARY OF THE INVENTION

The present invention is an improvement in the exothermic, liquid phasereaction of C₄ and C₅ isoolefins with themselves to form oligomers,preferably dimers, and with C₁ to C₆ alcohol to form ethers by contactin a fixed bed catalyst of acidic cation exchange resin, wherein theimprovement is the operation of the reactor at a pressure to maintainthe reaction mixture at its boiling point within the range of 120degrees F. to 300 degrees F. whereby at least a portion but less thanall of said reaction mixture is in the vapor phase.

This is a substantial departure from the prior art for this type ofreactor, where sufficient pressure was employed to maintain the reactionmixture in liquid phase.

A given composition, the reaction mixture, will have a different boilingpoint at different pressures, hence the temperature in the reactor iscontrolled by adjusting the pressure to the desired temperature withinthe recited range. The boiling point of reaction mixture thus is thetemperature of the reaction and the exothermic heat of reaction isdissipated by vaporization of the reaction mixture. The maximumtemperature of any heated liquid composition will be the boiling pointof the composition at a given pressure, with additional heat merelycausing more boil up. The same principal operates in the presentinvention to control the temperature. There must be liquid present,however, to provide the boil up, otherwise the temperature in thereactor will continue to rise until the catalyst is damaged. In order toavoid exotherms which will vaporize all of the reaction mixture, it isnecessary to limit the amount of isoolefin in the feed to the reactor toabout 60 wt.% of the total feed.

The present reaction can be used on streams containing small amounts ofthe isoolefin, however, feed to the reaction will need to be preheatedto near the boiling point of the reaction mixture, since lowconcentrations of isoolefin (1 to 8 wt. %) do not provide a very greatexotherm (i.e., as noted above the prior art used diluents to controlthe temperature in the liquid phase reaction). In any event it may benecessary to preheat the feed to the reaction such that temperature ofthe reaction, i.e., the boiling point of the reaction mixture (feedtemperature plus exotherm) is in the range of 120° F. to 300° F., whichrepresents the desirable range for the equilibrium reactions at apressure in the range of 0 to 400 psig.

The catalyst bed may be described as a fixed continuous bed, that is,the catalyst is loaded into the reactor in its particulate form to fillthe reactor or reaction zone, although there may be one or more suchcontinuous beds in a reactor, separated by spaces devoid of catalyst.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simple reactor operated in a quasi-isothermal manner.

FIG. 2 is a modification where the heat of the reaction is recovered topreheat the feed to the reactor, i.e., operated quasi-isothermally andadiabatically.

DETAILED DESCRIPTION OF THE INVENTION

The temperature in the reactor is thus controlled by the pressure used.The temperature in the reactor and catalyst bed is limited to theboiling point of the mixture present at the pressure applied,notwithstanding the magnitude of the exotherm. A small exotherm maycause only a few percent of the liquid in the reactor to vaporizewhereas a large exotherm may cause 30-90% of the liquids to vaporize.The temperature, however, is not dependent on the amount of materialvaporized but the composition of the material being vaporized at a givenpressure. That "excess" heat of reaction merely causes a greater boil up(vaporization) of the material present.

Although the reaction is exothermic, it is necessary to initiate thereaction, e.g., by heating the feed to the reactor. In prior reactorssuch as the tubular reactors the temperature of the temperature of thereaction (bed) may be controlled with the heat exchange medium; i.e.,either adding or removing heat or removing heat as required. In anyevent once the reaction is initiated an exotherm develops and must becontrolled to prevent a runaway reaction or damage to the catalyst.

The reaction product (ethers, dimers, unreacted feed) in the presentinvention is at a higher temperature than the feed into the reactor witha portion being vapor and a portion liquid. The reactor is operated at ahigh liquid hourly space velocity (5-20 LHSV, preferably 10-20) to avoidthe reverse reaction and polymerization of the olefins present in thefeed). Under these conditions high conversion of feeds, containing 5 to30 weight percent isoolefins are obtained, e.g., 80-90% conversion andsomewhat lower conversions for stream containing higher concentrationsof the isoolefins.

Thus, it may be desirable to have two and possibly more of the presentreactors in series to obtain higher conversions of the isoolefins. Insuch a case the product from the first reactor will normally be cooled,by heat exchange to obtain the desired temperature in the secondreactor.

Conveniently the feed to the first reactor is used to cool the productfrom the first reactor prior to its entry into the second reactor, hencethe heat of reaction supplies some of the heat necessary to initiate thereaction in the first reactor. This method of recovering the heat ofreaction can also be used where a single reactor is employed. Hence thereactor, or reactors can be operated in a substantially adiabaticmanner.

The product from either a single reactor or a series of reactorsoperated quasi-isothermally as taught here may be separated byconventional distillation, by recovering oligomer or the ether as abottom product and unreacted feed components as overheads, withappropriate water washing to remove or recover any alcohol (methanol andethanol form azeotropes with the unreacted C₄ and C₅ feed streamcomponents).

However, a further embodiment of the present invention is thecombination of the present reaction operated in fixed bed in partialliquid phase (as described) with a catalytic distillation using anacidic cation exchange resin as the distillation structure. This has theadvantage of further reacting the residual isoolefins whilefractionating the reaction product concurrently to produce even higherconversion of the isoolefins. This combination has a further advantagein that both catalyst beds, i.e., the fixed partial liquid phase reactorand the catalytic distillation reactor can be relatively small comparedto the use of either bed alone when used to obtain the same level ofisoolefin conversion obtained by the combination.

Another advantage of the combination is that the small partial liquidphase bed can serve as a guard bed for the distillation column reactorbed, since catalyst poisons (metal ions and amines) even if present inparts per billion will deactivate the acidic cation exchange resin intime. The small guard bed can be easily and less expensively replaced asit is deactivated while the life of the catalytic distillation bed maybe extended several years.

Catalysts suitable for the present process are cation exchangers, whichcontain sulfonic acid groups, and which have been obtained bypolymerization or copolymerization of aromatic vinyl compounds followedby sulfonation. Examples of aromatic vinyl compounds suitable forpreparing polymers or copolymers are: styrene, vinyl toluene, vinylnaphthalene, vinyl ethylbenzene, methyl styrene, vinyl chlorobenzene andvinyl xylene. A large variety of methods may be used for preparing thesepolymers; for example, polymerization alone or in admixture with othermonovinyl compounds, or by crosslinking with polyvinyl compounds; forexample, with divinyl benzene, divinyl toluene, divinylphenylether andothers. The polymers may be prepared in the presence or absence ofsolvents or dispersing agents, and various polymerization initiators maybe used, e.g., inorganic or organic peroxides, persulfates, etc.

The sulfonic acid group may be introduced into these vinyl aromaticpolymers by various known methods; for example, by sulfating thepolymers with concentrated sulfuric acid or chlorosulfonic acid, or bycopolymerizing aromatic compounds which contain sulfonic acid groups(see e.g. U.S. Pat. No. 2,366,007). Further sulfonic acids group may beintroduced into these polymers which already contain sulfonic acidgroups; for example, by treatment with fuming sulfuric acid, i.e.,sulfuric acid which contains sulfur trioxide The treatment with fumingsulfuric acid is preferably carried out at 0° to 150° C. and thesulfuric acid should contain sufficient sulfur trioxide after thereaction so that it still contains 10 to 50% free sulfur trioxide.

The resulting products preferably contain an average of 1.3 to 1.8sulfonic acid groups per aromatic nucleus. Particularly, suitablepolymers which contain sulfonic acid groups are copolymers of aromaticmonovinyl compounds with aromatic polyvinyl compounds, particularly,divinyl compounds, in which the polyvinyl benzene content is preferably1 to 20% by weight of the copolymer (see, for example, German Patentspecification 908,247).

The ion exchange resin is preferably used in a granular size of about0.25 to 1 mm, although particles form 0.15 mm up to about 1 mm may beemployed. The finer catalysts provide high surface area, but also resultin high pressure drops throughout the reactor. The macroreticular formof these catalysts is preferred because of the much larger surface areaexpose and the limited swelling which all of these resins undergo in anon-aqueous hydrocarbon medium.

Similarly, other acid resins are suitable, such as perfluorosulfonicacid resins which are copolymers of sulfonyl fluorovinyl ethyl andfluorocarbon and described in greater detail in DuPont "Innovation",volume 4, No. 3, Spring 1973 or the modified forms thereof as describedin U.S. Pat. Nos. 3,784,399; 3,770,567 and 3,849,243.

The resin catalyst is loaded into a reactor as a fixed bed of thegranules. The feed to the reaction is fed to the bed in liquid phase.The bed may be horizontal, vertical or angled. Preferably the bed isvertical with the feed passing downward through the bed and exiting,after reaction, through the lower end of the reactor.

For the present oligomerization and etherification reactions, the feedmay be a C₄ or C₅ containing stream, for example, a C₄ or C₅ refinerycut, although a mixed stream could be employed. In addition to C₄, sucha C₄ stream may contain small amounts of C₃ and C₅ and a C₅ will containsmall amounts of C₄ and C₆, depending on the precision of the refineryfractionation.

Isobutene is the C₄ isoolefin and it dimerizes to produce diisobutene.Some higher oligomers are produced as well as some codimers withn-butenes that are normally present in a C₄. The dimerization is thepreferential reaction because the two most reactive molecules arecombining. Higher polymers result from the continued contact of thedimer with isobutene in the presence of the catalyst. At the high LHSV(low residence time) employed for the present reaction, little polymeris formed.

Isoamylene has two isomers, i.e., 2-methyl butene-1 and 2 methylbutene-2, both of which are normally present in a C₅ stream. Both arehighly reactive and the dimer product is a mixture of the three possibledimers.

Both the isobutene and isoamylene preferentially react with alcohols inthe presence of an acid catalyst, hence only small amounts of dimer orother oligomerization products are produced when the etherification iscarried out.

The C₁ to C₆ alcohol for the etherification may be fed to the reactorwith the hydrocarbon stream or by a separate feed. The methanol ispreferably fed at the upstream end of the reactor to inhibitoligomerization of the olefins and to preferentially react with morereactive isoolefins to form ethers.

The alcohol, e.g., methanol may be and is preferably present in astoichiometric amount of the isoolefin present although an excess of upto 10%, may be desirable. In addition slightly less than astoichiometric amount may be employed. It should be appreciated that theskilled chemist will optimize the proportions and precise conditions foreach particular piece of equipment and variation in catalyst, once thebasic invention is comprehended. The alcohols employed are those having1 to 6 carbon atoms. Preferred are those having one hydroxyl group.Preferred alcohols include methanol, ethanol, propanol, n-butanol,tertiary butanol, 1-pentanol, 2-pentanol, 3-pentanol, 1-hexanol,2-hexanol, 3-hexanol, cyclopentanol and hexanol. A preferred grouping ofalcohols are those having 1 to 4 carbon atoms and one hydroxyl group.

The alcohols may be used alone or in mixtures of any proportion toproduce highly complex ether products having unique properties as octaneimprovers for gasoline or as solvents.

The reaction in the fixed bed is primarily a liquid phase reaction, butunlike all other known liquid oligomerizations and etherificationsreactions carried out in this manner, no attempt is made in the presentprocess to maintain a completely liquid phase. Since the reaction isexothermic, the pressure in the reactor is adjusted to maintain thedesired temperature which allows some portion of the material to bevaporized. The reactor may be said to run in a quasi-isothermal manner.

EXAMPLE 1

Referring to FIG. 1, a simple reactor 10, packed with acidic cationexchange resin catalyst 12 is shown. The reactor was pilot plant sizeand contained a 10 foot by 2 inch diameter bed of Amberlyst 15 Beads.

The feed was of refinery C₄ cut admixed with methanol and entered thereactor via line 14. The feed had been preheated to 138° F., and flowedthrough the resin bed and exited via line 16. The feed entering thereactor was in liquid phase and the product exiting was partiallyvaporized. The conditions and results of this run are summarized inTABLE I. Conversion of isobutene 89.7%.

The recovered stream 16 would normally be subjected to furthertreatment, by way of fractionation to separate the unreacted C₄ from theether and to recover the unreacted methanol. The product stream 16 cango directly into a distillation column (not shown) where the heat of thereaction is utilized in the distillation.

EXAMPLES 2 and 3

In FIG. 2 modification of the simple procedure of FIG. 1 is illustrated.The feed, a refinery C₄ stream, enters heat exchangers 50 via line 60where it indirectly contacts product from reactor 52 which enters theheat exchanger via 54. Once the reaction is started the product exitingthe reactor is at a higher temperature than the feed and is used to heatfeed entering the reactor via line 56. As in FIG. 1, the feed is amixture of the C₄ 's and methanol. After the indirect contact of thereaction product and feed in the heat exchange 50 the cooled productexits via line 58.

Operated in this manner the feed to reactor is at a temperature near theexotherm, hence the reactor is operating under near adiabaticconditions.

The net heat of reaction of the system is the difference between thetemperature of the feed into the system and the product out of thesystem, i.e., 45° F., which is about the same as for the simple systemillustrated in FIG. 1 (since the feeds are similar). The conditions andresults of the two runs with two different C₄ feeds are illustrated inTable II using the system of FIG. 2. It should be noted that the feed ofExample 3 contained a higher isobutene content than Example 1. Since thepressure was the same for both examples the exotherm for Example 3 washigher. In order to have reduced the temperature in Example 3, thepressure would have needed to have been reduced, since the compositionin the reactor had changed.

In either embodiment (FIG. 1 or FIG. 2) the product stream may be passedto a second or subsequent quasi-isothermal reactor and the processrepeated. This would be expedient when the isoalkene is greater thanabout 30% of the feed, since conversion would be low on a per passbasis. Also, as shown in FIG. 2, the product stream 58 may be fed to adistillation tower 62 where the ether product is recovered as a bottoms64 and unreacted feed stream components and methanol recovered asoverhead 66.

Alternatively, tower 62 may be catalytic distillation tower where theresidual isoalkene is reacted with residual methanol (or added methanolto produce extremely high conversions of the isoalkene in a single passthrough the system (e.g. 95%+). The packing in a catalytic distillationcolumn is described in the above noted patents, but briefly, it has beenfound that placing the resin beads into a plurality of pockets in acloth belt, which is supported in the distillation column reactor byopen mesh knitted stainless steel wire by twisting the two together,allows the requisite flows, prevents loss of catalyst, allows for thenormal swelling of the beads and prevents the breakage of the beadsthrough mechanical attribution.

The cloth may be of any material which is not attacked by thehydrocarbon feed or products under the conditions of the reaction.Cotton or linen are useful, but fiber glass cloth or "Teflon" cloth arepreferred. A preferred catalyst system comprises a plurality of closedcloth pockets arranged and supported in said distillation column reactorand supported in said distillation column reactor by wire meshintimately associated therewith.

The particular catalytic material may be a powder, small irregularfragments or chunks, small beads and the like. The particular form ofthe catalytic material in the cloth pockets is not critical, so long assufficient surface area is provided to allow a reasonable reaction rate.This sizing of catalyst particles can be best determined for eachcatalytic material (since the porosity or available internal surfacearea will vary for different materials, and, of course, affects theactivity of the catalytic material).

For the present oligomerizations and etherifications, the catalyst isthe same type, an acidic cation exchanged resin, used in the continuousbed reactors.

It should be appreciated that the same mechanism of allowing excess heatof reaction to merely create boil up has been employed in both thecontinuous bed rectors and in the catalytic distillation. Although asnoted above, continuous bed reactors have been disclosed to operate fordifferent process in a quasiisothermal manner the operation of a liquidphase etherification in this manner is in direct conflict with all ofart on the subject.

In the three examples of the present invention given here approximately30% of the feed in the continuous bed quasiisothermal reactor wasvaporized. In Examples 2 and 3 the product 54 leaving the heat exchangerwas all liquid, however, in some operations according to the presentinvention, depending on the temperature and composition of stream 54, aportion may still be in the vapor state.

The heat exchanger 62 should be sized, such that an amount of heat equalto the heat of reaction in reactor 52 is allowed to pass through,otherwise the heat in the reactor will build up. An alternative means isto provide a by pass, shown by dashed line 55 whereby a portion of theeffluent from the reactor is by passed around the heat exchanger toobtain the same result.

In the oligomerization, just as in the etherification, the tertiaryolefins are more reactive and tend to form oligomers, primarily dimers,e.g., diisobutene, some higher oligomers and some codimers with normalolefins. The oligomerizations are run under the same general conditionsas the etherifications with the oligomer products being the heaviercomponent of the product stream. In fact, it may be desirable in someoperations to switch between the two reactions, by adding or withholdingthe alcohol as desired.

                  TABLE I                                                         ______________________________________                                                       Line 14      Line 16                                           ______________________________________                                        Conditions                                                                    Temp., °F.                                                                            138          185                                               Press., psig   --           150                                               LHSV 11.9                                                                     ______________________________________                                                       lbs/hr  wt %     lbs/hr                                                                              wt %                                    ______________________________________                                        Composition                                                                   Isobutene      15.6    14.6      1.6   1.5                                    Other C4's     79.4    74.2     79.4  74.2                                    Methanol       12.0    11.2      4.0   3.7                                    MTBE           --      --       22.0  20.6                                    Conversion of isobutene                                                                      89.7%                                                          ______________________________________                                    

                                      TABLE II                                    __________________________________________________________________________    Example 2               + Example 3                                           Conditions                                                                           Line 60                                                                           Line 56                                                                           Line 54                                                                           Line 58                                                                            + Line 60                                                                           Line 56                                                                           Line 54                                                                           Line 58                                 __________________________________________________________________________    Temp., °F.                                                                    90  170 185 135  + 90  186 201 156                                     Press., psig                                                                         --  --  150 150  + --  --  150 150                                     LHSV 10.2                                                                     __________________________________________________________________________    Composition                                                                          lbs/hr                                                                            wt. %                                                                             lbs/hr                                                                            wt. %                                                                              + lbs/hr                                                                            wt. %                                                                             lbs/hr                                                                            wt. %                                   __________________________________________________________________________    Isobutene                                                                            13.1                                                                              14.2                                                                               0.9                                                                               1.0                                                                               + 21.8                                                                              20.4                                                                               3.8                                                                               3.6                                    Other C4's                                                                           66.9                                                                              72.7                                                                              66.9                                                                              72.7                                                                               + 68.2                                                                              63.7                                                                              68.2                                                                              63.7                                    Methanol                                                                             12.0                                                                              13.1                                                                               5.0                                                                               5.4                                                                               + 17.0                                                                              15.9                                                                               6.7                                                                               6.3                                    MTBE   --  --  19.2                                                                              20.9                                                                               + --  --  28.3                                                                              26.4                                    Conversion of isobuten - 93.1%                                                                        + Conversion of isobutene - 82.6%                     __________________________________________________________________________

What is claimed is:
 1. An improvement in the process of the exothermic,liquid phase reaction of C₄ or C₅ olefins with themselves to formoligomers thereof by contacting a downflow stream containing up to 60weight percent of said olefins with a vertical fixed bed catalystcomprising an acid cation exchange resin at a temperature in the rangeof 120° F. to 300° F. in a reactor to form a reaction mixture containingoligomers, wherein the improvement comprises the operation of saidreactor at a pressure to maintain said reaction mixture in said reactorat its boiling point within the range of 120° F. to 300° F. whereby atleast a portion but less than all of said reaction mixture is vaporized,said reaction occurring in said liquid phase portion, and all of saidreaction mixture is recovered as a single stream exiting through thelower end of the reactor.
 2. The process according to claim 1 wherein apredominantly C₄ hydrocarbon stream from 1 to 60 weight percentisobutene is contacted with said fixed bed catalyst.
 3. The processaccording to claim 2 wherein the pressure in the reactor is in the rangeof 0 to 400 psig and the LHSV of said stream is in the range of 5 to 20.4. The process according to claim 3 wherein mixture contains unreactedC₄ hydrocarbon and a predominant of diisobutene.
 5. The processaccording to claim 4 wherein said stream is preheated by indirect heatexchange contact with the reaction mixture from said reactor.
 6. Theprocess according to claim 1 wherein a predominantly C₅ hydrocarbonstream containing from 1 to 60 weight percent isoamylene is contactedwith said fixed bed catalyst.
 7. The process according to claim 6wherein the pressure in the reactor is in the range of 0 to 400 psig andthe LHSV of said stream is in the range of 5 to
 20. 8. The processaccording to claim 7 wherein said reaction mixture contains unreacted C₅hydrocarbon and a predominent amount of dimers of isoamylene.
 9. Theprocess according to claim 8 wherein said stream is preheated byindirect heat exchange contact with the reaction mixture from saidreactor.
 10. The process according to claim 1 wherein said stream ispreheated prior to contact with said catalyst.
 11. The process accordingto claim 1 wherein said reaction mixture is passed to a distillationcolumn reactor containing an acid cation exchange resin in a pluralityof pockets in a cloth belt supported in said distillation column reactorby open mesh knitted stainless steel wire to further react saidisoolefins with themselves to form oligomers thereof.